Long term evolution (LTE) technology is the 4G (fourth Generation) of wireless cellular communication technology. The LTE technology adopts orthogonal frequency division multiplexing (OFDM) technology, in which time-frequency resources constituted by subcarriers and OFDM symbols make up radio physical resources of a LTE system. At present, the OFDM technology has been widely applied in wireless communications. A CP-OFDM system adopting a cyclic prefix (CP) can shorten the multipath delay well, and divides a frequency selective channel into a set of parallel flat channels, which simplifies the channel estimation method well, and achieves a high accuracy in channel estimation. However, the performance of the CP-OFDM system is sensitive to frequency shifts, that is, Doppler shifts, which is mainly due to the large spectrum leakage of the system. This can easily cause inter-carrier interference (ICI). Moreover, the CP also occupies time resources and reduces the spectral efficiency.
Nowadays, companies begin to study the 5G (Fifth Generation) of wireless communication technology, in which filter bank-based multicarrier offset quadrature amplitude modulation (FBMC-OQAM) technology may be adopted. In the case where the subcarriers are distributed at equal intervals, the length of a symbol in the FBMC-OQAM is half the length of a symbol in OFDM. The FBMC-OQAM is also called OFDM-OQAM in some documents. The FBMC-OQAM uses a proper pulse shaping function to filter, reducing out-of-band leakage and better countering effects of frequency shifts and Doppler shifts. Moreover, the FBMC-OQAM does not require the use of the CP, which also helps to increase the spectral efficiency.
However, for an actual faded channel, inherent interferences exist between the subcarriers and between the symbols of the FBMC-OQAM system. In particular, there are large interferences between adjacent subcarriers and between adjacent symbols, which will seriously affect thee channel estimation performance of a receiving terminal and further affect the demodulation of data. An original channel estimation method of the CP-OFDM system may not be directly used in the FBMC-OQAM system. Accordingly, a pilot frequency of the FBMC-OQAM system needs to be specially designed and a different channel estimation method should be adopted accordingly.
There are several channel estimation methods of the FBMC-OQAM system in the related art. One method is to use null data symbols to separate pilot symbols from data symbols, so as to reduce the interference of the data symbols on the pilot symbols, and further improve the channel estimation performance. However, in such a setting method, the pilot signal overhead is high. Furthermore, in the case of multiple antennas, multiple null data symbols are needed to separate the pilot symbols of each antenna, which further makes the pilot signal overhead high. Moreover, the channel estimation performance is poor in this method. Another method is to use an auxiliary pilot to cancel the interference of surrounding data on pilot data. If the number of auxiliary pilots is small, the power of the auxiliary pilots will be large in order to cancel out the interference. However, large power of the auxiliary pilots will affect the peak-to-average ratio of the signal. On the contrary, if the number of auxiliary pilots is large, it will lead to a high pilot overhead, and the channel estimation performance is poor in such a setting method. Accordingly, it is eager to providing a good pilot signal design method and a corresponding channel estimation method in the FBMC-OQAM system.
In other filter bank-based multicarrier (FBMC) systems, such as a Generalized Frequency Division Multiplexing (GFDM) system, it is also necessary to provide a good pilot signal design method and the corresponding channel estimation method. Accordingly, it is required to propose a good pilot signal design method commonly used for as many systems based on time-frequency physical resources as possible.